Chemical and biological agents (or contaminants) pose many adverse effects and health threats to humans and animals. These contaminants may be in a fluid form (e.g. gas, liquid, or gel) or a solid form (e.g. powder). Chemical contaminants include nerve agents, blister/percutaneous agents, and blood agents. Nerve agents attack human body and interfere with nervous system via immobilization of key enzymes. Blister/percutaneous agents attack the skin and/or mucous membranes tissues external and/or internal to human body. Biological contaminants include bacteria, viruses, fungi and spores, which may also attack human body. Thus, these harmful chemical and biological contaminants have to be filtered and/or eliminated so as to prevent them from attacking human body.
Face masks with limited filtering capacity, such as N95 and surgical masks, are commonly used to protect human from pathogens. These face masks and normal filters neither detoxify chemical contaminants nor disinfect biological contaminants. Hence, various filtration techniques and products have been explored and introduced to eliminate chemical and/or biological contaminants. Such a protective material is described for example in US 2010/0113857 A1, which discloses a nano-sized fiber comprising metal oxide nanoparticles for detoxifying a toxic agent. The weight ratio of metal oxide nanoparticles to polymer of the nanofiber is about 1:10. Another example is described in US 2008/0264259 A1, which discloses a filtration medium that includes a fine filter layer and a coarse filter layer. The fine filter layer comprises anti-microbial nanoparticles of about 0.1 weight percent (wt %) to 10 wt %.
For the above examples and other prior art, the content of the detoxifying material in a filtration medium is relatively low (e.g. below 15 wt %) and may be toxic. Hence, it is important to prevent leaching of this material from the medium. It is important to note that simply increasing the loading of the detoxifying material in a filtration medium without careful considerations of the structure of the filtration medium and the processes of making the filtration medium would lead to leaching of the detoxifying material which is undesirable. Further, it is not easy to synthesize a uniform or homogenous nanofiber layer from a solution with high loading of a detoxifying material. Hence, a need exists for a filtration medium with highly improved detoxification efficiency and at the same time does not impose any risks and adverse effects to the users of the filtration medium.